By Jim Kerr

The price of fuel just jumped again! Economy cars and hybrids are looking better all the time, and engine cylinder de-activation systems are one of the technologies that may help with those rising fuel costs.

Currently, three vehicle manufacturers are offering cylinder de-activation system engines for the Canadian market. Chrysler was first to the marketplace with their MDS (Multiple Displacement System) Hemi engines. GM and Honda were not far behind. GM calls theirs Displacement on Demand or DOD, while Honda refers to theirs as Variable Cylinder Management (VCM).

Each of these systems has pros and cons. The Chrysler system is perhaps the simplest to implement, but is as effective as the other two. When Chrysler was designing the Hemi V8 engine, they were already thinking of cylinder deactivation. Every production 5.7 litre Hemi block was already cast with the necessary configuration to enable it to be upgraded to MDS operation with only a few machining operations. By adding eight special hydraulic lifters, four solenoids and a sensor, Chrysler could economically and quickly add the system.

2006 Dodge Ram 1500 with Chrysler Group's Multi-displacement System (MDS)
2006 Dodge Ram 1500 with Chrysler Group’s Multi-displacement System (MDS). Photo: DaimlerChrysler. Click image to enlarge

With the introduction of the MDS Hemi engine in the 2006 Ram 1500 pickup, truck owners will be able to take advantage of this system just like car owners did in the past couple years. Estimated fuel economy improvements of up to 20% can be achieved under some driving conditions.

“By 2007, Chrysler Group will have nearly one-million vehicles on the road with MDS,” said Eric Ridenour, Executive Vice President – Product Development, Chrysler Group. “And 60 million gallons of fuel will be saved annually with the Hemi engine’s MDS technology.”

So what does cylinder deactivation do? It simply turns off some of the cylinders so they don’t consume fuel. All the current designs deactivate half the cylinders. On a V8, the engine runs on 4 cylinders. On Honda’s V6, it runs on three. To accomplish this, the fuel injection is turned off, and the valves are stopped for those cylinders. Chrysler and GM use electric solenoids that control oil flow to special hydraulic lifters. When the oil is turned off, the lifters unlock, taking up the movement of the camshaft inside the lifter instead of moving the valve.

2006 Honda Odyssey illustration: Variable Cylinder Management (VCM) components
2006 Honda Odyssey illustration: Variable Cylinder Management (VCM) components. Image: Honda. Click image to enlarge

Honda uses their VTEC technology to unlock rocker arm movement from the camshaft to prevent valves from opening. Honda is also using this technology on the latest Civic Hybrid to deactivate cylinders during deceleration so maximum electrical power can be generated and stored in the battery for later use.

I had concerns about different amounts of wear on those cylinders that were working all the time compared to those turned off. According to all the engineers I talked to, from all three manufacturers, there is no appreciable difference in cylinder to cylinder wear patterns. The
cylinders are only de-activated during light load conditions, where little stress is placed on the rings, pistons and cylinder walls. To reduce wear, the systems do also activate all the cylinders occasionally to keep the engine block warm evenly.

Having driven all the systems, I can tell you the switch from all the cylinders operating to only half producing power and back again is seamless. Even drivers paying sharp attention to engine operation would have difficulty detecting the switch over. Electronic throttle control keeps the engine rpm and torque output constant as it switches.

Eight cylinders operate on four cylinders smoothly. Operating a six-cylinder engine on three requires a little more technology to keep the vehicle smooth. Honda uses special motor mounts and a noise cancellation system in their audio system to eliminate any droning or exhaust pulsation noises from the vehicle interior.

While you may not want to rush out and buy a V8 engine with cylinder deactivation just to save fuel costs, drivers who need the hauling capacity and power will benefit from this technology. What interests me is the possibility of adapting this technology to four cylinder engines in the future, where it could operate on two cylinders for light city cruising and all four for acceleration. It hasn’t been demonstrated yet to the public, but I am sure the engineers are working on this behind the scenes.

There are many different ways to achieve better fuel economy. Cylinder de-activation is only one method, but it has the ability to provide both good fuel economy and good power in the same vehicle.

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